JPS6412351B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for suppressing the pool swell phenomenon that occurs during a loss of coolant accident in a boiling water nuclear reactor.

[Conventional technology]

Figure 1 shows a boiling water nuclear reactor called a Mark type, and Figure 2 shows a boiling water reactor called a Mark type. Although the shapes of the containment vessels 1 and 1' are different between the two, the basic structures of both are as follows.

The containment vessel 1, 1' is divided into a dry well 2, 2' and a suppression chamber 6, 6'.
The reactor pressure vessels 7, 7' are provided within the dry wells 2, 2'.

Suppression pools 5, 5' are provided at the lower portions of the suppression chambers 6, 6', and the upper portions thereof are wet wells 4, 4'.

The dry wells 2, 2' and the suppression pools 5, 5' are communicated through steam discharge pipes 3, 3'. The steam release pipes 3, 3' are used to store the differential pressure between the dry wells 2, 2' and the wet wells 4, 4' when the emergency core cooling system is activated and the pressure inside the dry wells 2, 2' is reduced. Vacuum break valves 10, 10' are provided to eliminate this.

Pool swell development in the event of a loss of coolant accident in the boiling water reactor containment vessel constructed as described above will be described next.

When a loss of coolant accident occurs, drywell 2,
The pressure inside 2' increases rapidly due to the steam released from the reactor pressure vessels 7, 7'. Then, from the lower ends of the steam release pipes 3, 3' into the suppression pool 5,
The air present in the dry wells 2, 2' is blown in, and bubbles are formed near the lower ends of the steam release pipes 3, 3'. These air bubbles act to push the pool water surface upward. Figure 3 shows the mark type (second
Figure) shows the effect of air bubbles. first water level 11
is pushed up by the air bubbles 12 like a rising water surface 13. Figure 4 shows temporal changes in the rate of rise of the pool water level. The horizontal axis is the elapsed time after the coolant loss accident occurred.

The above is a phenomenon called pool swell, and the gas discharged from the steam discharge pipes 3, 3' initially contains a lot of air, but gradually changes to water vapor. Since the water vapor is condensed by the suppression pools 5, 5', the pressure within the dry wells 2, 2' is reduced.

[Problem to be solved by the invention]

The pool swell phenomenon described above exerts an impact load on each member constituting the pressure vessel as described below.

a Underwater structures and underwater walls are under pressure due to the formation and rapid growth of bubbles.

b Due to the accelerated rise in the water surface, structures above the water surface are subjected to water impact.

c. As the pool water level rises, the pressure inside the wet wells 4, 4' increases, so the wet well walls also receive pressure load.

FIG. 5 shows an example of pressure changes that the dry well 2 and wet well 4 undergo during pool swell. 14 is a curve showing the pressure inside the dry well 2, and 15 is a curve showing the pressure inside the wet well 4. It is recognized that there are times when the wetwell pressure curve 15 is higher than the drywell pressure curve 14. At this time, the vacuum breaker valve 10 described above opens and closes rapidly, which may cause wear and tear on the valve seat surface.

In the case of the mark type shown in Fig. 3, the water level rising due to the pool swell phenomenon reaches the ring header 9.
Impact loading on the vehicle is also a serious problem. FIG. 6 is a diagram of the pressure curve 16 applied to the ring header. In order to alleviate such an impact force, it may be considered to provide a deflector 33 below the ring header 9 as shown in FIG. 3, but this alone is not sufficient to alleviate the impact load caused by the pool swell.

In the case of the mark type shown in FIG. 1, the diaphragm floor 30 is
Applying upward pressure on the market can also pose a danger.

Conventionally, measures have been taken to prevent damage caused by the pool swell phenomenon, such as increasing the strength of the aerial structure above the suppression pool 5 and improving the durability of the vacuum breaker valve 10. , which is uneconomical due to increased manufacturing costs.

The present invention has been made in view of the above circumstances, and suppresses the pool swell phenomenon that occurs in the suppression chamber in the event of a coolant loss accident, and alleviates the impact load that is applied to each member constituting the storage container. The purpose is to

[Means to solve the problem]

Next, the basic principle of the present invention will be explained with reference to FIGS. 7 to 9.

A double cylindrical suppression cylinder 17 consisting of an outer cylinder 17a and an inner cylinder 17c is installed in the suppression pool 5.

17b is the bottom wall of the outer cylinder 17a, and the inner cylinder 17
c passes through this. However, in the present invention, penetration means that the spaces above and below the bottom wall are communicated through an inner cylinder, and the inner cylinder does not need to protrude below the bottom surface.

The lower end of the inner cylinder 17c is opened below the normal water level 8 of the suppression pool 5,
The upper end 17c ₁ of the inner cylinder 17c is opened above the water surface 8.

The upper end 17a ₁ of the outer cylinder 17a is opened higher than the upper end 17c ₁ of the inner cylinder 17c.

With this configuration, the outer cylinder 17a and the inner cylinder 17
Pool water does not flow into the space 18 formed between the pool and the pool c.

[Effect]

FIG. 8 shows the initial state of pool swell generation. When the pool water level 19 rises due to the generation of air bubbles 21, the water level 1 in the inner cylinder 17c increases accordingly.
9' also rises, overflowing from the inner cylinder 17c as shown by arrow A and flowing into the space 18. Then, the water depth H pushed up by the bubbles in the inner cylinder 17c decreases, so the water in the inner cylinder 17c is pushed up at an accelerated rate, and the boundary surface 20' between the bubbles and water in the inner cylinder 17c becomes
The bubbles rise faster than the boundary surface 20 outside the cylinder, and after a short time, as shown in FIG. 9, the bubbles reach the upper end of the inner cylinder 17c. Then, the air that has formed bubbles 21 under the water surface is exhausted into the wet well 4 above the pool water surface 19 as indicated by arrow B through the inner pipe 17c.

In this way, the force of the bubbles pushing up the pool water surface 19 disappears, and the water that was being pushed up falls by gravity. Therefore, the rise in water level due to pool swell is alleviated, the maximum water level rise limit is significantly lower than in conventional devices, and the maximum water level rise rate is also significantly lower.

As mentioned above, the rise in the pool water level is alleviated because (a) the inner cylinder 17c is set vertically at a position where it intersects with the normal water level of the suppression pool, and (b) the steam inner cylinder is placed outside. Penetrating the bottom wall 17b of the cylinder,
This is the overall effect of the fact that a space 18 is formed between the inner and outer cylinders, and (c) that the upper end 17a ₁ of the outer cylinder is located higher than the upper end 17c ₁ of the inner cylinder.

Therefore, as mentioned above, air bubbles 2 under the water surface
1 is exhausted into the wet well 4 through the inner cylinder 17c, and the water level rise is more effectively alleviated by installing the inner cylinder 17c almost vertically so as to protrude slightly above the normal water level 8. Space 1 on the outer periphery
This is an effect of forming an exhaust passage for the air bubbles 21 by providing the outer cylinder 17a through the outer cylinder 8.

〔Example〕

FIG. 11 shows one embodiment of the invention. In this embodiment, a pool swell suppressing cylinder 17 having the structure described above is installed in a mark-shaped suppression chamber 6'.

The pool swell suppressing cylinder 17 is
8, 28 to the steam discharge pipe 3'. Pool swell suppression tube 1 in this embodiment
7, in addition to mitigating the rise in the pool water level as described above, the rising water level directly flows into the ring header 9.
It also acts as a deflector to prevent collisions.

FIG. 12 shows the pool swell suppressing cylinder 17 mentioned above.
This is an embodiment in which a mark type suppression chamber 6 is provided. The upper end of the pool swell suppressing cylinder 17 is fixed to the diaphragm floor 30, and the center and lower part thereof are fixed to the diaphragm floor 30 by a placing 28'.
It is attached to the steam discharge pipe 3 via. Reference numeral 29 is a vent hole for communicating the inside of the suppressing cylinder 17 and the wet well 4.

FIG. 13 shows an improved example of the pool swell suppressing cylinder shown in FIG.
1 is provided and is attached to the outer tube 17a by a support 32. The guide vane 31 is connected to the inner cylinder 17c.
It is created in a shape that guides water spouted up in the directions of arrows C and C to the space 18 as shown by arrows D and D.

Various examples can be considered as the shape of such a guide vane, such as a conical shape with the apex facing downward, a pyramid shape, or a roof shape with the ridgeline facing downward.

When the guide vanes 31 are provided above the inner tube 17c as described above, the water ejected upward from the inner tube is efficiently caused to flow into the space 18, so that the pool swell suppressing action is performed quickly and smoothly.

FIG. 14 shows the above-mentioned pool swell suppressing tube 17.
A pool swell suppressing cylinder 17' having a structure similar to that of
In this embodiment, two steam discharge pipes 3 are attached to each steam discharge pipe 3 by placing 28'.

FIG. 15 shows an embodiment different from the above, in which the inner cylinder 17c'' of the pool swell suppressing cylinder 17'', which is similar to that explained with reference to FIG. 7, has a larger diameter than the inner cylinder 17c of the previous example, and the outer The diameter of the cylinder 17a'' is also increased, the steam release pipe 3 is inserted into the inner cylinder 17c'', and the placings 33 and 34 are attached to integrate the steam release pipe 3, the inner cylinder 17c'', and the outer cylinder 17a''. It is attached to. This embodiment has great strength as a structure.

FIG. 10 is a chart comparing the change in the pool water level in the conventional device when a coolant loss accident occurs and the change in the pool water level in the embodiment shown in FIG. 11 described above.

The horizontal axis is the time axis, and t ₀ is the time point when the loss of coolant accident occurs. Curve 24 represents the rate of rise in the pool water level in the conventional device, and curve 25 represents the rate of rise in the water level in the pool swell suppression pipe in the embodiment described above.Curve 2
6 is the rising speed of the pool water level outside the pool swell suppression pipe in the same example.

At the very beginning of pool swell generation, the rate of rise of the water level inside the suppression pipe 25 in the above embodiment begins to accelerate rapidly, similar to the rate of rise of the water level outside the pipe 26, but as described above, it increases at an accelerated rate and the water level outside the pipe increases. Climb speed 26
will be faster than.

Point _t1 on the time axis is when the water level in the pipe reaches the upper end of the inner pipe 17c, that is, when the state shown in FIG. 9 described above is reached. At this time point _t1 , the water in the inner pipe 17c flows into the space 18, so the acceleration of the water level rise rate becomes slower. After a short period of time, the bubbles are exhausted into the wetwell 4 through the inner tube 17c, so that the out-of-tube water level rise rate 26 begins to slow down after a short period of time. Therefore, the maximum value V ₁ of the pool water level rise rate 26 outside the pipe in this embodiment is significantly lower than the maximum value V ₂ of the pool water level rise rate 24 in the conventional device. Therefore, the impact force caused by the rising water surface is much smaller.

〔Effect of the invention〕

As explained above, the device according to the present invention is applied to a boiling water reactor containment vessel, in which a double cylindrical member consisting of an almost vertical inner cylinder and an outer cylinder is installed in a suppression pool, The above-mentioned outer cylinder has a bottomed structure, and the inner cylinder penetrates the bottom surface.The lower end of the above-mentioned inner cylinder is located below the normal water level of the suppression pool, and the upper end of the outer and inner cylinders is It is located above the normal water level of the suppression pool, and the upper end of the outer cylinder is located above the upper end of the inner cylinder, so it alleviates the rise in pool water level due to pool swell phenomenon and prevents the same phenomenon. As a result, the impact load that each member receives can be significantly reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view of a known mark-type containment vessel, Fig. 2 is a schematic partial cross-sectional view of a known mark-type containment vessel, and Fig. 3 shows the pool swell phenomenon within the mark-type containment vessel. Figure 4 is a diagram of the water surface rising speed during pool swell, Figure 5 is a diagram of pressure change, Figure 6 is a diagram of impact load, and Figures 7 to 9 are cross-sectional views showing the state that is occurring. Figure 10 is an explanatory diagram of the basic configuration and operation of the present invention.
The figure is a diagram showing the effect of suppressing the pool swell phenomenon in one embodiment of the present invention, and FIG. 11 is a cross-sectional view of one embodiment in which the present invention is applied to a mark-type containment vessel.
FIG. 12 is a sectional view of an embodiment in which the present invention is applied to a mark-type storage container, and FIGS. 13 to 15 are sectional views of embodiments different from the above. 1, 1'... Containment vessel, 4, 4'... Wet well, 5, 5'... Suppression pool, 8...
...Normal water level of suppression pool, 17,1
7', 17''...pool swell suppression tube, 17a,
17a″...outer cylinder of pool swell suppression cylinder, 17
c, 17c″...Inner cylinder, 31...Guide blade.

Claims (1)

[Claims] 1. In a boiling water reactor containment vessel, a double cylindrical member consisting of an almost vertical inner cylinder and an outer cylinder is installed in a suppression pool, and the outer cylinder has a bottom. In this structure, an inner cylinder passes through the bottom surface of the inner cylinder, and the lower end of the inner cylinder is opened below the normal water level of the suppression pool, and the upper end of the inner cylinder is opened below the normal water level of the suppression pool. A pool swell suppression device in a boiling water reactor containment vessel, characterized in that the outer cylinder is opened above the water level, and the upper end of the outer cylinder is opened above the upper end of the inner cylinder. 2. The boiling water type according to claim 1, characterized in that a guide vane is provided above the inner cylinder to guide water ejected from rising inside the inner cylinder to the outside of the inner cylinder. Pool swell suppression device in reactor containment vessel.